Conventionally, for devices for carrying out graphical representation of measurement results and analysis results, a technique for partially enlarging a graph is proposed (for example, refer to JP H11-066330(A)). The graphical representation device of JP H11-066330(A) specifies the enlarging range by a rectangular window displayed in the graph. The enlarging range is specified by a user specifying a position and a size of the window using a mouse.
However, the specifying technique of the enlarging range proposed in JP H11-066330(A) is not suitable for the conventional fish finders. FIG. 1 is a view showing an example of an image display of echo data in the conventional fish finder. In FIG. 1, an example of dual screen image constituted with a normal entire screen image on the right side and an enlarged screen image thereof on the left side is shown.
As shown in FIG. 1, many images indicative of echo data (a school of fish, etc.) and noises are displayed in the screen of the fish finder. The echo data are generally displayed in a darker color as their reflection intensity becomes higher. For this reason, if the user tries to specify the enlarging range by the rectangular window, the window overlaps with the images of high-intensity echo data; thereby user's visual recognition will be greatly deteriorated. In addition, the conventional fish finder does not display common results which are fixedly displayed in a graph, but it time-sequentially displays echo data per one longitudinal line of the display screen at a time to update the screen image by line. Therefore, the user must determine the enlarging range referring to images of new echo data which are updated every moment while taking a depth displayed in the screen into consideration, not specifying the enlarging range by including only the past images already displayed.
For example, as shown in FIG. 1, a case where an upper end and a lower end of the enlarging range are specified by Line 1 and Line 2 which are displayed in the normal entire screen image is considered. Here, it is assumed that a school of fish B is newly displayed by the update when the user is about to specify the enlarging range on the basis of a school of fish “A” which is already displayed near the center of the screen. In this case, the user probably specifies the upper end and the lower end of the enlarging range taking depths of the two schools of fish into consideration. However, in this case, Line 2 overlaps with the image of the school of fish B and Line 1 overlaps with images of noises and a depth scale and, thus, the enlarged image is very bad in visual recognition. In addition, specifying of a lateral width may also be required in fact for some cases, which further deteriorates the visual recognition.
As described above, the window possibly overlaps with the images of echo data in many cases in the conventional fish finders. Therefore, it is difficult to specify a desired enlarging range only by the technique of simply specifying a desired position in the graph by the rectangular window like JP H11-066330(A).